1. Field of the Invention
The invention relates to a method for operating a pulse width modulated (“PWM”) output of a driver for a power semiconductor.
2. Description of the Related Art
Power semiconductors, for example IGBTs (Insulated Gate Bipolar Transistors), usually require a driver for actuation. The driver converts a low-power logic signal into a high-power switching signal which can then be supplied directly to the switching input of the power semiconductor, e.g., the gate of the IGBT, and ultimately switches the power semiconductor.
In this case, a driver usually performs various ancillary functions in addition to its actual switching function under certain predetermined conditions. For example, a variable having an analog value, such as temperature or voltage, may be measured on the power semiconductor or a yes/no error signal, i.e., a binary supplementary value is produced if the driver or semiconductor fails. Common voltage values in this case are in the range of from approximately 0V to approximately 10V, for example. Both an analog value of this kind and a binary supplementary value are output by the driver. For this purpose, the latter usually outputs the analog value in the form of a PWM output signal. The binary value is output at an additional output. A customer using the driver connects the relevant outputs according to the requirements of the application for further processing of the signals applied thereto. In other words, the output is followed by a transmission link for the circuit logic required by the customer.
The analog value is converted into a PWM signal at a fixed PWM frequency within the driver. In this case, the PWM output has a first (Hi) and a second (Lo) signal level for the PWM signal, between which the PWM output alternates. Since the transmission link also has only the two signal levels, it can be understood to be digital and can be implemented by means of optical fibers, for example. In other words, the analog value to be transmitted or the analog signal is converted into a PWM signal at a fixed frequency by a transmitter. The longer the signal level is Hi within a PWM clock cycle, the higher the analog value to be transmitted.
At the receiver end, i.e., at the end of the transmission link, for example in the circuit connected by the customer, a receiver in turn outputs a defined level for the respective one of the two signal levels. In this case, the receiver may be implemented either in analog form or in digital form. In the case of an analog receiver, a low-pass filter, such as an RC element, is used to smooth the received PWM signal into an analog output value, for example. In the case of digital evaluation, the receiver samples the PWM signal at a known frequency. In this case, the sampling rate of the receiver determines the accuracy thereof.
It is a known practice for the binary supplementary value to be transmitted separately on a second transmission link, which likewise has two signal levels, e.g., a second optical fiber.
While known systems work satisfactorily in most circumstances, there is always a need for improved performance.